Chromatography is the term used to describe the various different types of laboratory processes that can be used to separate mixtures. All types of chromatography involve separating a mixture between a mobile phase and a stationary phase. The mixture is on the stationary phase (a solid or a liquid) and the mobile phase (fluid) is passed through it. Chromatography can be preparative or analytical. The purpose of Preparative chromatography is to separate the components to be used for other purposes. Analytical chromatography aims to measure the relative proportion of the analyte in the mixture.
The different types of chromatography can be categorized into five different sections: Adsorption, Partition, Ion Exchange, Molecular Exclusion, and Affinity. Here, we will focus on Adsorption.
Adsorption
Adsorption Chromatography is the process where a mobile gas or liquid solute accumulates onto the surface of a stationary solid, forming a thin layer of molecules. Unlike other types of chromatography, adsorption is usually a liquid-on-solid extraction. First, the sample that is to be tested is placed on the solid, called the adsorbent. The adsorbent is a solid that is capable of binding the components on it into a mixture. Next, the solid is dipped into a solvent (such as H2O). As the solvent travels up the solid, it meets and dissolves the sample, creating the adsorbate. Then, it will continue up the paper as a solvent solute sample. Different compounds in the sample will result in the solute traveling at different rates, depending on the solubility of the solvent, and the attraction between the solvent and the solid. With relation to chemical dyes, the compounds that make up the dyes will behave differently, which would easily distinguish them between each other.
In this experiment, adsorption is used to seperate the different compounds in chemical dyes. The adsorbent is chromatography paper, the solute is the coloured pigment, and the solvent is the Isopropyl Alcohol. Once the solvent reaches the solute, the adsorbate is formed. However, there are many different compounds in each couloured pigment. If one of the compounds has low solubility, that specific adsorbate will travel faster up the chromatography paper. This is because the low solubility results in a longer time as a liquid solution, which in turn results in a longer time travelling upwards via capillary action. Consequently, a higher solubility equals a shorter time going upwards. This would, in turn, show the dispersion of different colours because of their various solubilities.
Paper Chromatography
Paper chromatography utilizes paper as the stationary phase and a liquid which doesn’t react with paper as the mobile phase. It is used primarily to separate and identify colored mixtures. For more complicated substances with similar compositions such as amino acids, two- way paper chromatography is recommended which uses two solvents.
The success of this type of chromatography is rooted in a solvents ability to move up paper by capillary action which is a result of the solvent molecules attraction to the paper and one to one another. The solvent rises up the paper, mixes with the sample mixture and continues to travel upwards. Due to differences in their attraction to the fibers in the paper and the differences in solubility in the solvent, different compounds travel upwards at different rates.
Rf (retention factor) values are used to determine particular components of the mixture. As long as the type of paper, exact composition of the solvent and other aspects of the experiment are consistent, the Rf value for a particular sample will always remain the same.
Rf is found using the following equation:
Distance travelled by sample
Distance travelled by solvent
Experiment
The purpose of this experiment is to demonstrate how paper chemotography can be utilized to separate inks or pigments.
Materials
6 Glass Jars
Chromatography Paper
Pencils
Rubbing alcohol (70% Isopropyl Alcohol)
Sharpie Pens of various colours
Measuring cup
Ruler
Scissors
Tape
Safety Goggles
Procedure
Measure approximately 15 mL of Isopropyl Alcohol and pour it in each jar.
Use the scissors and ruler to cut 6 equally long strips of Chromatography Paper. Then, in pencil, draw a horizontal line 1 cm above the bottom edge of each strip.
Using each Sharpie pen, place a spot along the line of the Chromatography Paper. Place no more than 3 spots on each strip. Write down all the colours and where each colour's spot is located.
Tape each strip onto a different pencil, and place the pencil onto the jar. Make sure that the strip of Chromatography Paper is touching the Isopropyl Alcohol inside, but does not pass the pencil line.
Let the strips develop until the ascending solution is approximately 2 cm from the top of the paper. Then remove the strips and let them air dry.
Record your observations and determine the retention factor.
Draft - Chromatographic Separation
Due 06 October, 2008Back to Period 2 - CS
Introduction
Chromatography is the term used to describe the various different types of laboratory processes that can be used to separate mixtures. All types of chromatography involve separating a mixture between a mobile phase and a stationary phase. The mixture is on the stationary phase (a solid or a liquid) and the mobile phase (fluid) is passed through it. Chromatography can be preparative or analytical. The purpose of Preparative chromatography is to separate the components to be used for other purposes. Analytical chromatography aims to measure the relative proportion of the analyte in the mixture.
The different types of chromatography can be categorized into five different sections: Adsorption, Partition, Ion Exchange, Molecular Exclusion, and Affinity. Here, we will focus on Adsorption.
Adsorption
Adsorption Chromatography is the process where a mobile gas or liquid solute accumulates onto the surface of a stationary solid, forming a thin layer of molecules. Unlike other types of chromatography, adsorption is usually a liquid-on-solid extraction. First, the sample that is to be tested is placed on the solid, called the adsorbent. The adsorbent is a solid that is capable of binding the components on it into a mixture. Next, the solid is dipped into a solvent (such as H2O). As the solvent travels up the solid, it meets and dissolves the sample, creating the adsorbate. Then, it will continue up the paper as a solvent solute sample. Different compounds in the sample will result in the solute traveling at different rates, depending on the solubility of the solvent, and the attraction between the solvent and the solid. With relation to chemical dyes, the compounds that make up the dyes will behave differently, which would easily distinguish them between each other.
In this experiment, adsorption is used to seperate the different compounds in chemical dyes. The adsorbent is chromatography paper, the solute is the coloured pigment, and the solvent is the Isopropyl Alcohol. Once the solvent reaches the solute, the adsorbate is formed. However, there are many different compounds in each couloured pigment. If one of the compounds has low solubility, that specific adsorbate will travel faster up the chromatography paper. This is because the low solubility results in a longer time as a liquid solution, which in turn results in a longer time travelling upwards via capillary action. Consequently, a higher solubility equals a shorter time going upwards. This would, in turn, show the dispersion of different colours because of their various solubilities.
Paper Chromatography
Paper chromatography utilizes paper as the stationary phase and a liquid which doesn’t react with paper as the mobile phase. It is used primarily to separate and identify colored mixtures. For more complicated substances with similar compositions such as amino acids, two- way paper chromatography is recommended which uses two solvents.
The success of this type of chromatography is rooted in a solvents ability to move up paper by capillary action which is a result of the solvent molecules attraction to the paper and one to one another. The solvent rises up the paper, mixes with the sample mixture and continues to travel upwards. Due to differences in their attraction to the fibers in the paper and the differences in solubility in the solvent, different compounds travel upwards at different rates.
Rf (retention factor) values are used to determine particular components of the mixture. As long as the type of paper, exact composition of the solvent and other aspects of the experiment are consistent, the Rf value for a particular sample will always remain the same.
Rf is found using the following equation:
Distance travelled by sample
Distance travelled by solvent
Experiment
The purpose of this experiment is to demonstrate how paper chemotography can be utilized to separate inks or pigments.
Materials
Procedure
Safety
Observations
Beyond the scope of this draft.
Analysis
Beyond the scope of this draft.